xSLX won’t work for you, the iClass readers use ISO14443a for their UID only mode.
If it’s an earlier model it specifies in the manual Mifare Classic (xM1, but not sure if it’ll still work with others) or if its an SE model it is any ISO1444a card including NExT and xNT.
Now, that’s hardware compatibility. Tap a Mifiare classic and an NTAG to the reader to know for sure. It could be turned on or off in the reader config. To change it is ordering a config card from HID and pulling the readers off the wall.
As for enrolling, you’ll have to tap and look at the number in the access logs, not just give them a tag info scan. There are about 5 different ways the system can represent the same data, so unless you know the exact reader config, you’ll have to tap to find out how it sends that number to the door controller.